The Dissolution Mechanism And Homogenized Behavior Of Modified Agent In The Process Of Blast Furnace Slag Fiber Forming

The blast furnace slag has the characteristics of large output and high residual heat grade.At present,the traditional blast furnace slag treatment method is mainly water quenching,which not only wastes a lot of waste heat,but also has a lower added value of slag resource utilization after water quenching.The composition of blast furnace slag is adjusted by adding a modified agent to improve the slag structure and physicochemical properties,and then the blast furnace slag fiber is prepared by using a centrifugal fiber forming process,and finally a fiber product is obtained,which can fully utilize the high-quality heat source of blast furnace slag,and can produce high value-added resource products.It is a new technology for comprehensive utilization of blast furnace slag.The blast furnace slag modified technology is the key factor for the direct fiber forming process of blast furnace slag.Especially in the modified process,the direct fiber formation of slag cotton fiber will lead to low fiber formation rate,high slag ball content and poor chemical stability when the modified agent is not dissolution completely or the composition of modified slag is not homogenized.For this problem,the CaO-MgO-SiO₂-Al₂O₃ quaternary slag system is mainly used.The dissolution mechanism and homogenization behavior of modified agent is studied by using FactSage thermodynamic software,microscopic analysis and thermal experiment.It is found that the dissolution process of iron ore waste rock is mainly SiO₂ dissolution,and There is an relation among the slag composition,temperature as well as SiO₂ particle size and dissolution time of SiO₂ in blast furnace slag are established.The evaluation criteria of the solid-liquid two-phase homogenization effect were established,and the relationship between the slag composition and the addition amount of iron ore waste rock and the homogenization time of the modified slag was established.The main results of this paper are as follows:There was an analysis on low fiber forming rate and high slag ball content after direct fiberization of the blast furnace slag from the aspects of fiber formation performance parameters,viscosity as well as crystallization.The results showed that in terms of fiber formation performance parameters,acidity coefficient and viscosity coefficient was low,the ion index was high.In terms of viscosity,the suitable temperature range of the blast furnace slag for fiber forming is 1351-1359?,the temperature range is narrow for 8?,which is difficult to control temperature,while the suitable temperature range of the modified slag for fiber formation is 1288-1397?,the temperature range is wide for 109?.In the aspect of crystallization,when the constant temperature of the blast furnace slag is1270°C during isothermal cooling process,the crystal incubation time is up to 186s,and the critical cooling rate is at least 0.74°C/s.However,as the constant cooling temperature of the modified slag is 1210°C,the crystal incubation time is up to 470s,the critical cooling rate is at least 0.30°C/s.In the continuous cooling process,in the case of completely solidifying into a glass state,the cooling rate of the blast furnace slag is greater than 6.5°C/s,and the cooling rate of the modified slag is greater than 2.5°C/s.Therefore,the modification of blast furnace slag can inhibit crystallization.In addition,the appropriate modification is analyzed from the aspects of melting performance and slag resistance,and the modification is determined to be iron ore waste rock.By the high temperature hot state test combined with SEM-EDS,it was concluded that the dissolution process of iron ore waste rock was mainly SiO₂ dissolution.Based on this,the dissolution process of SiO₂ in slag system was observed by high temperature confocalmicroscopyandtherewereastudyontheinfluenceofslag composition,temperature,and SiO₂ particle size on the dissolution rate and dissolution time of SiO₂ in blast furnace slag.It was concluded that,with slag basicity for 1.1,MgO content for 11%,and Al₂O₃ content for 18%,the time for the complete dissolution of SiO₂particles was the shortest.The solid state diffusion coupler combined with the theory of blast furnace slag molecular structure was applied to clarify the dissolution mechanism of SiO₂ particles.The dissolution kinetic model of SiO₂ particle was constructed based on the shrinkage nucleus model.The control of the SiO₂ particle dissolution reaction was clarified,and dissolution reaction kinetic parameters of SiO₂ particle was obtained.Firstly,the homogenization process of the modified slag was characterized by the change rule of viscosity.The SiO₂ content determination and the mineral phase analysis method were used to verify the method which confirmed that the method of viscosity determination of the homogenization behavior of modification blast furnace slag was feasible.With the increase of slag basicity and MgO content,the homogenization time of modified slag was shorter while the homogenization time of modified slag was prolonged as Al₂O₃ content increased.With the increasing addition of iron ore waste rock,the homogenization time of the modification blast furnace slag was larger.After the amount of the modification is more than 20.94%,that is,the acidity coefficient parameter of the modified slag is more than 1.3,there is a linear growth between the addition amount of the iron ore waste rock and homogenization time of the modified slag.Through semi-industrial tests,it is shown that the modified slag is centrifuged into fiber after homogenization,and the fiber forming rate is obviously improved.As the acidity coefficient grows,the increasing value of the fiber forming rate is gradually increased with the maximum increase value of 26.1%,but after the acidity coefficient exceeds 1.4,the added value tends to be stable.Through the study on the diameter,slag ball content,acid and alkali resistance properties and crystallization performance of blast furnace slag fiber after homogenization,it is found that with the increase of acidity coefficient,the diameter and slag ball content of blast furnace slag fiber are gradually improved as well as acid and alkali resistance properties.Nevertheless,the crystallization tendency firstly decreased and then increased,and the crystallization tendency was the at the lowest point when the acidity coefficient was 1.2.Based on that,the evolution regularity of blast furnace slag fiber crystallization phase was analyzed.The crystallization kinetics of blast furnace slag fiber was established by combining Ozawa equation and modified Kissinger equation.Under different acidity coefficients,the growth factor and activation energy of blast furnace slag fiber were obtained.In addition,the thermal damage mechanism of the fiber was clarified by analyzing the crystallization rate,the crystallization phase content and the particle size of the blast furnace slag fiber.